Omnirange beacon antenna having rotating parasitic conductive elements



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OMNRANGE BEACON ANTENNA HAVING R- TATING PARASITIC CONDUCTIVE ELEMENTS lled Jan. 5, 1955, Ser. No. 479,882

8 Claims. (Cl. 343-761) This invention relates to onmirange beacon antennas and more particularly to directive antenna systems for producing a multiple modulation radiation pattern having a fundamental modulation frequency and one or more additional harmonics of the fundamental modulation frequency for use with omnidirectional beacons.

Omnidirectional beacon systems are known having a very high directional accuracy which are dependent upon the use of a rotating antenna pattern of a generally cardioid shape rotated at a fundamental frequency and modulated by a harmonic of this fundamental frequency so as to produce a generally multilobed rotating directive antenna radiation pattern. Due to the rotation of the special antenna pattern, a receiver located remotely from the transmitter receives energy which appears as an amplitude modulated wave having a fundamental modulation component and a modulation component at a harmonic frequency of said fundamental. Both fundamental and harmonic frequency reference signals are also transmitted omnidirectionally for comparison with the received components of the rotating pattern so that the receiver may determine its azimuth relative to the beacons antenna system.

Previous antennas designed for use with such omnidirectional beacons have necessitated the use of rotating radiofrequency (R.-F.) joints or have been difficult to enclose for weather protection. Other known antenna systems have disclosed the production of the modulation frequency by the rotation of a parasitic element about a vertical stack of central radiators such as cones.

One of the objects of this invention therefore is to provide an improved omnidirectional beacon antenna system especially suited for use in the radiation ot a rotating multilobed directive radiation pattern.

Another object of this invention is to provide an antenna system for producing a multilobed azimuthal directive pattern which may be completely enclosed so as not to be aifected by weather elements.

A further object of this invention is to produce an antenna system for radiating a multilobed rotating directive radiation pattern without the use of rotating R.-F. joints.

In accordance with one of the features of this invention, a single rotating metal disk is used to form a support structure for parasitic modulation elements and to also provide counterpoise action for said elements. A vertical stub antenna radiates energy which is modulated by the rotating parasitic elements disposed at least at two different distances from said radiator to provide a directive multilobed radiation pattern for use in an omnidirectional beacon system.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following descriptiontaken in conjunction with the accompanying drawings, in which:

Fig. l is a view in perspective of one embodiment of the omnidirectional beacon system of this invention; and

Fig. 2 is a sectional view `of the embodiment of the States antenna system taken along the lines 2--2 of Fig. 1 illustrating the arrangement of the center radiator unit and the feed system.

Referring to Figs. l and 2 of the drawing, an antenna system for producing a rotating multilobed shaped azimuth directivity pattern comprises a central radiator 1 supported at the center of a `rotating disk 2. A harmonic frequency series of parasitic elements 3 spaced at regular angular intervals are atiixed to the surface of an outer rot-ating liberglass housing 4 while a fundamental frequency group of parasitic elements 5 is attached to an inner fiberglass housing 6.

Referring more specically to Fig. 2 of the drawing, a source of radio-frequency (R.-F.) energy is coupled to a coaxial transmission line 10 having an inner conductor .10a and an outer conductor 10b. The inner conductor 10a is coupled to a central radiator 1 which essentially comprises a quarter wavelength vertical stub antenna. The outer conductor 10b has its direction reversed to form a skirt 13 spaced from the central radiator 1 as shown by the distance d. A rotating metal disk Z functioning as a counterpoise surrounds the central radiator assembly. A quarter wavelength choke generally indicated at 14 is provided so that there is no leakage of energy as the metal disk 2 rotates. Surrounding the central radiator assembly l is an inner berglass housing 6. The fundamental frequency parasitic group of elements is carried by the inner fiberglass housing 6 which rotates about the central .radiator l. The elements 5` are insulated from the counterpoise 2 by insulation 12. Also rotating with the metal disk counterpoise 2 is an outer fiberglass housing 4 on which a plurality of parasitic element groups 3 are carried for the harmonic modulation. The metal disk 2 providing a planar surface functioning as a counterpoise is rotated by means of a mo-tor 21. The rotating metal disk 2 is separated `by a quarter Wavelength choke generally indicated at 14 4from an extension of the counterpoise assembly i7 which surrounds the rotating portion of the antenna system. The choke joint 11 at the center of the disk 2 is incorpo-rated in order to prevent complications such as rotating R.F. joints in the feed line 10 of the central .radiator 1, thus allowing the central radiator l to remain stationary while the disk assembly 2 is rotating. It is apparent that parasitic elements can be placed on the rotating disk 2 in any way necessary to produce the desired modulation frequencies. As shown in Fig. 1, the parasitic elements 5 carried by the inner fiberglass housing 6 produce a lfundamental modulation having a frequency equal to the `frequency of the disks rotation. It is apparent that each individual parasitic element in the group comprises a portion of conductive material above and perpendicular to the rotating disk and a portion parallel to the rotating disk. It is also to be noticed that the parasitic elements 5 are insulated from the counterpoise 2. The arrangement of the harmonic parasitic elements 3 provides means for tuning each'element for a maximum current by varying the length of element above and below the counterpoise 2 and also provides a means for lowering the center of radiation of the unit so that the radiation may be directed with increasing amplitude at increasing vertical angles.

The harmonic modulation parasitic elements 3 are placed at properly chosen distances in accordance with the Bessel function expansion and are shown in Fig. l as being carried by the outer fiberglass housing 4 coupled to rotating disk 2 in order to provide the harmonic modulation of the fundamental frequency. The counterpoise 2 is extended beyond the outer fiberglass housing 4 in order that the radiation pattern will have a marked differential in radiated energy between vertical angles above the horizon and those below the horizon. The extension 17 of the counterpoise 2 is supported by means of weather- 3 proof housing 20. The greater the extension of the counterpoise 2 beyond the harmonic parasitic elements 3, the greater the differential in the signal directed above the horizon to that directed below the horizon. It is,

-of cou-rse, understood that it is highly desirable in an omnrange beacon antenna to have a large differential between the vertical angles above and below the horizon in order to allow the beacon to be sight free. The choke joint 14 is provided between the rotating portion of the counterpoise 2 and the extended skirt portion 17 in order to prevent a system having a large diameter from rotating. However, it is, of course, apparent that the outer choke joint 14 is not mandatory Ifor purposes of this invention since an extension of the counterpoise beyond the harmonic parasitic elements 3 is not only practical, but will provide an appreciable tip-tilt to the radiation pattern.

While we have described above the principles of our invention in connection with specic apparatus, it is to be clearly understood that this description is made only by way of example and notas a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claims.

We claim:

1. An antenna system comprising a conductive member having a planar surface, a radiator vertically disposed centrally of said surface and a plurality of parasitic conductive elements disposed in an electrically insulated relationship with said member for rotation about said radiaror.

2. An antenna system comprising conductive means presenting a counterpoise surface, a radiator vertically disposed centrally of said surface, a plurality of parasitic conductive elements electrically insulated from and carried by said means with at least parts thereof above said surface, and means to rotate said means to cause said elements to rotate about said radiator.

3. An antenna system comprising a conductive member having a part suitable as a counterpoise surface, a radiator vertically disposed centrally of said surface, at least one dielectric cylinder carried yby said member concentrically of said radiator, a plurality of parasitic conductive elements carried by said cylinder and means to rotate said cylinder about said radiator.

4. An antenna system comprising a conductive member having a planar surface, a radiator vertically disposed centrally of said surface, a plurality of dielectric cylinders carried by said member concentrically of said radiator, a rst group of parasitic conductive elements carried by one of said cylinders and a second group of parasitic conductive elements carried by another of said cylinders and means to rotate said cylinders about said radiator.

5. An antenna system comprising a conductive member having a planar sur-face, a radiator vertically disposed centrally of said surface, a rst group of parasitic conductive elements electrically insulated from and carried by said member disposed at a iirst distance from said radiator, a second group of parasitic conductive elements concentric to said rst group electrically insulated from and carried by said member and disposed at a second distance from said radiator and means to rotate said members.

6. An antenna system comprising a conductive member having a planar surface having an inner area, a middle area and an outer area, the adjacent rims of each of said areas being anged to form radio-frequency chokes, a radiator vertically disposed centrally of said surface, a first group of parasitic conductive elements carried by said middle area disposed about said radiator and a second group of parasitic conductive elements concentric to said rst group carried by said middle area and means to rotate said middle area.

7. An antenna system comprising a conductive member having a planar surface, a radiator vertically disposed centrally of said surface, a plurality of dielectric cylinders carried by said member disposed concentrica-lly about said radiator, a iirst group of parasitic conductive elements carried by one of said cylinders and disposed vertically to said surface and a second group of parasitic conductive elements carried by another of said cylinders disposed vertically to said surface and means to rotate said cylinders about said radiator.

S. An antenna system comprising a conductive member having an upper annular surface, a 'radiator vertically disposed coaxially of said annular surface, a first and second dielectric cylinder each carried by said member and disposed concentrically about said radiator, a irst parasitic element assembly including a single group of conductors carried by the first of said cylinders and a. second series of elements comprising a plurality of groups of conductors carried by the second of said cylinders and means to rotate said member and cylinders about said radiator.

References Cited in the le of this patent UNITED STATES PATENTS 2,243,523 Davis May 27, 1941 2,640,930 Lundburg June 2, 1953 2,670,436 Dunbar Feb. 23, 1954 2,717,379 Earp Sept. 6, 1955 2,726,389 Taylor Dee. 6, 1955 2,753,554 Adams et al. July 3, 1956 2,770,800 Lundburg Nov. 13, 1956 2,803,821 Pickles et al. Aug. 20, 1957 2,846,677 Stavis Aug. 5, 1958 

